Method of making variable area sound film with low background noise



Patented Nov. 30, 1937 UNITED STATES PATENT orrics METHOD OF MAKING VARIABLE AREA' 'SOUND FILM WITH LOW BACKGROUND NOISE 'No Drawing. Application February 6, 1935,

Serial No. 5,259. In

6 Claims.

The present invention relates to a method of reducing ground noise in sound film and per tains particularly to a method for reducing the residual ground noise after the development of the positive film.

It has been suggested previously in the art to so develop sound films made by the variable density method and to so treatthem in a photographic reducing agent that a positive film is ch- 10 tained which exhibits linear blackening or density increase starting with perfect transparency.

The present invention consists in treating in a photographic reducer sound-films made by the variable area or the multi-peak method, both of 5 which, in contradistinction to variable density sound tracks and films, consist of portions presenting maximum'blackening and unblackened portions. This method is useful both in connection with negative as well as positive sound films as well as with both.

The object of the invention is to provide a film,

particularly a film of variable area type, having.

a minimum of ground noise in relation to the particular negative film from which it has been reproduced. 7

Another object of the invention is to provide a film having a minimum of ground noise from discreet silverparticles in the transparent portion thereof.

In the practical application of the method suggested in the present invention, local blackened portions of small size which are found in the transparent parts of a variable area sound track film and which are causative of what is known as the background ,(film) noise, are bleached out with the result that the said noise otherwise occurring with full force inreproduction or projection is lessened.

With the identical end in view, it has hereto- I 40 fore been customary in the use of variable area sound films to so shift the zero line of the sound track as a function of the sound volume that the transparent portions of the positive film strip become as small as possible; or else recourse was had to the step to cover or mask a variable area film made in the usual way with a straight zero line, either during the recording or subsequently a Germany May 8, 1934 or cutting reducer as such a reducer decreases the background noise in a much greater proporto tank development is preferable for motion picture film such, for example, as the mercury and the cyanide reducer or the iodine cyanide reducer described in the aforesaid publication.

It is recommended that sound films which are to be reduced according to the present invention, be exposed and/or developed somewhat more strongly than is done in the case of normal films in order that the action of the reducing agent upon the thoroughly blackened portions of the film may be without an efiect' upon the reproducing sound volume.

Having thus described my invention, I claim:

1. The method of making variable area sound film comprising the step of subjecting the posltive film after development to the action of'a reducing agent.

2. The method of making sound films comprising the step of subjecting the positive film to the action of a subtractive reducing agent.

3. The method of making sound films of the variable area type comprising the step of subjecting the film to the action of a reducing agent which will reduce the density in the less dense portions thereof by a larger percentage than the density in the more dense portions.

4. The method of making variable area sound film, comprising the step of subjecting the negative film after development to the action of a reducing agent.

5. The method of making sound films, comprising the step of subjecting the negative film *to the action of a subtractive reducing agent.

6. The method of making a-low background noise variable area sound film, comprising the step or subjecting the negative film after development to the action of a reducing agent and thereafter subjecting the positive film after development to the action of a reducing agent.-

\ ROLF GoRIscH. 

